I come from the car world. I did an sdsefi system on a turbo 4Runner I built years back. They had this coarse mixture knob to allow you to make large swings to overall a/f ratios. It's really only mean't for initial tuning, once you have the system dialed in, it shouldn't be needed. I have tuned a lot of fuel injected stuff, both factory ecm's and stand-alones. The sds is not a bad system, but is clunky to work with and adjust in my opinion.The other advantages (usually) are, no choke, no carb heat (on this type of injection) and usually no mixture control. I'm kind of baffled with this one - as in their 7th picture down, they show and describe a "mixture knob". What for? On any efi system the primary advantage is the computer is supposed to be selecting mixture automatically - it's how the efficiency is usually gained. SO I don't know what the knob would be for or what the computer really does, if you still manually adjust mixture?
The benefits to FI in a plane would be, no carb heat to worry about, no mixture knob to worry about. Theoretical best a/f ratios regardless of temp, altitude etc. More accurate mixture equals more power/efficiency. Now I say theoretical because there is still room for error based on the tune and some other factors. But it's real close when done right.
And wether you have an efi system you can tweak (tuning wise) or a carb with a mixture knob, in my opinion they should have a wideband a/f gauge. This allows you to actually see in real time what a/f's your running at, and do something about it if it's off.